Abstract Although emerging evidence suggests that low levels of vitamin D may contribute to the development of autoimmune disease, the relationship between vitamin D reduction and autoimmune thyroid disease AITD, which includes Graves’ disease GD and Hashimoto thyroiditis HT, is still controversial. The aim was to evaluate the association between vitamin D levels and AITD through systematic literature review. We identified all studies that assessed the association between vitamin D and AITD from PubMed, Embase, CENTRAL, and China National Knowledge Infrastructure CNKI databases. We included studies that compared vitamin D levels between AITD cases and controls as well as those that measured the odds of vitamin D deficiency by AITD status. We combined the standardized mean differences SMD or the odds ratios OR in a random effects model. Twenty case-control studies provided data for a quantitative meta-analysis. Compared to controls, AITD patients had lower levels of 25OHD SMD: −0.99, 95% CI: −1.31, −0.66 and were more likely to be deficient in 25OHD OR 2.99, 95% CI: 1.88, 4.74. Furthermore, subgroup analyses result showed that GD and HT patients also had lower 25OHD levels and were more likely to have a 25OHD deficiency, suggesting that low levels of serum 25OHD was related to AITD. View Full-Text